An experimental study on fine structures of supersonic laminar-turbulent flow over a backward-facing step based on NPLSReportar como inadecuado




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Chinese Science Bulletin

, Volume 57, Issue 6, pp 584–590

First Online: 28 January 2012Received: 05 July 2011Accepted: 02 September 2011

Abstract

Fine structures of supersonic flow over a 5 mm high backward facing step BFS, including expansion wave fan, reattachment shock, supersonic boundary layer were measured in a Ma=3.0 low-noise indraft wind tunnel. By varying the superficial roughness of the wall upstream from the step, supersonic laminar flow and supersonic turbulent flow could be formed over a BFS. Measurements on the spatiotemporal features of the holistic flow field and the fine structures in four typical regions were carried out using NPLS nano-based planar laser scattering. Flow structures, including expansion wave fan, reattachment shock, supersonic boundary layer and its separation, reattachment and redevelopment are revealed by measuring the holistic structure of the transient flow field. Comparing the two time-averaged flow fields with each other, it is apparent that supersonic turbulent flow over a BFS STF-BFS has a larger expansion angle and a shorter recirculation region, and its redeveloped boundary layer increases at a smaller obliquity while the angle of reattachment shock is the same for the supersonic laminar flow over a BFS SLF-BFS. With regard to time-evolution features, the K-H vortices in the SLF-BFS suffers from shearing, expansion, reattachment and three-dimensional effects while in the STF-BFS large-scale structures are affected by the incline and distortion at the reattachment point due to expansion, viscosity and reverse-pressure. Studies on local regions indicate that in the SLF-BFS, the emergence of compression waves which distinctly converge into a reattachment shock is due to the local convective Mach number and the inducement of K-H vortices in the free shear layer. Nevertheless, in the STF-BFS, compression waves and K-H vortices are barely evident, and the formation of a reattachment shock is related to the wall compressive effect.

Keywordssupersonic flow over a backward facing step nano-based planar laser scattering fine structure laminar turbulent This article is published with open access at Springerlink.com

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Autor: Zhi Chen - ShiHe Yi - Lin He - LiFeng Tian - YangZhu Zhu

Fuente: https://link.springer.com/article/10.1007/s11434-011-4888-y







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